Tuesday  |  Frick  |  10:00 AM–10:20 AM

#13612, Advancement of EBSD Towards Measuring Absolute Stress Fields

A novel and accessible technique to measure high-resolution stress fields may provide fundamental understanding of the many intricate grain boundary deformation mechanisms and may open up new pathways to design novel high-performance alloys. To this end, the High-angular-Resolution Electron Backscatter Diffraction (HR-EBSD) method, in which elastic strain is measured from correlation of EBSD patterns (EBSPs), needs extension. In absolute HR-EBSD, a simulated EBSP is used as reference, yet the accuracy is troubled by calibration of the experimental geometry and simulation of all experimental EBSP features. In contrast, relative HR-EBSD is much more accurate (elastic strains ∼1E-4), yet requires one EBSP in each grain as reference, thus only yielding relative stress levels in each grain.

First, we explore a concept where a stress-free reference point is obtained by creating a so-called ‘Ring Core’ using focused ion beam milling [1]. Using the commercially available ‘Cross-Court’ software for relative HR-EBSD, EBSP’s outside the Ring Core are correlated to a reference EBSP inside the stress-free pillar of the ring core. This method, being validated with a home-built setup for controlled bending of a silicon wafer, shows great promise.

Second, we extend our previously proposed non-simulation-based, absolute HR-EBSD approach [2,3] based on Integrated Digital Image Correlation (IDIC) of the EBSP’s, which takes full advantage of plane stress assumptions and crystal symmetry. For numerically generated EBSPs, high absolute stress accuracy (elastic strain resolution <1E-4) is obtained in all grains of a virtually stressed polycrystalline microstructure [3]. However, experimental validation shows the importance of accurately capturing the so-called ‘excess-deficiency’ effect in the Kikuchi bands, for which the IDIC framework is adapted. Validation of this extended non-simulation-based, absolute HR-EBSD approach will be presented at the SEM2022.

[1] T. Vermeij, E. Plancher, C. C. Tasan. "Preventing damage and redeposition during focused ion beam milling: the “umbrella” method." Ultramicroscopy 186 (2018): 35-41.
[2] T. Vermeij, J.P.M. Hoefnagels. "A consistent full-field integrated DIC framework for HR-EBSD." Ultramicroscopy 191 (2018): 44-50.
[3] T. Vermeij, M. DeGraef, J.P.M. Hoefnagels. "Demonstrating the potential of accurate absolute cross-grain stress and orientation correlation using electron backscatter diffraction." Scripta Materialia 162 (2019): 266-271.

Johan Hoefnagels   Eindhoven University of Technology
Marcos Rodríguez Sánchez   Eindhoven University of Technology
Lloyd Dodswordth   Eindhoven University of Technology
Luca Palmeira Belotti   Eindhoven University of Technology
Tijmen Vermeij   Eindhoven University of Technology